A “rim joist” or “band joist” of a building structure's floor rests on a sill or a sill plate and functions to keep the floor's joists true. The rim joist also provides a surface for completing the edge of subflooring and a flat base from which to support exterior walls. The rim joist forms a first wall of a rim joist cavity or “box,” while adjoining floor joists extending generally perpendicularly away from the rim joist form second and third walls of the box. A subfloor typically forms a top of the box, while the sill or sill plate forms a bottom of the box. An opening opposite the rim joist provides access to the box.
The rim joist can be a significant source of drafts, especially in older building structures with stone and masonry foundations. Drafts are often pulled from the rim joist and through the structure, into openings provided for plumbing pipes, electrical conduit and the like. By sealing off the rim joist box and the various openings the comfort level for occupants of the building structure can be increased and energy costs for the building structure can be reduced.
A relatively efficient way to insulate a rim joist box is to utilize a suitable expanding-foam insulation. To install the expanding-foam insulation a suitable resin and a foaming agent are typically brought together within a mixing chamber of an applicator gun to produce the expanding-foam insulation. The mixture of insulating foam is then quickly injected or is otherwise dispensed into the rim joist box through the opening of the box. Upon entering the rim joist box the insulation material, which is usually in the form of a relatively heavy lather, rapidly expands in volume to at least partially fill the box. The insulation, once cured, sets up into a generally uniform insulative structure to provide a thermal and/or acoustical barrier.
A drawback of using expanding-foam insulation to fill a rim joist box is that the insulation is subject to overflowing out the opening of the box during the expansion phase of the insulating foam, resulting in wasted insulation material and producing an unsightly appearance. Prior efforts to limit this overflow have been attempted by using cardboard or string restraints to close off the opening. However, insulating rim joint boxes in this manner is a messy proposition and often still leads to an unprofessional finished appearance. There is a need for a way to efficiently and effectively install expanding-foam insulation.